DETROIT -- Prized first-round draft pick Eric Ebron is day to day with an undisclosed injury and his status for Saturday's preseason opener against the Cleveland Browns is unknown.

"He has an injury," coach Jim Caldwell said after a practice Wednesday night at Ford Foeld. "We'll keep him out for a couple days and see how he does.

"We'll see (if he can play against Cleveland). He's day to day, so we'll see how it goes."

Ebron hadn't missed a practice through rookie minicamp, OTAs, minicamp and the first eight days of training camp. He practiced Tuesday, but showed up at Ford Field on Wednesday donning a baseball cap and shorts.

He did not participate in the workout, which the Lions generously estimated 4,488 people attended. A Lions spokesperson whisked Ebron off the field after practice, telling reporters the tight end had "a commitment."

Caldwell later emphasized Ebron's injury is "nothing serious," which suggests his availability for the start of the regular season isn't threatened.

But with only three days until the Cleveland game, it seems likely Detroit will opt to hold out Ebron as a precaution. His much-anticipated debut could be delayed until next week's game in Oakland against the Raiders.

That's a blow for a player who says he's still not comfortable in the offense.

Ebron is being asked to line up mostly in the slot, as well as in-line, in the backfield and even split out wide. That should make him a versatile weapon in the long-term, but also means he has a lot to learn in the short term.

The Lions also practiced without Corey Greenwood, who had an "excused absence." Caldwell said he wasn't certain whether the linebacker would be back Thursday.

Receiver TJ Jones and defensive end Ezekiel Ansah remain on the physically unable to perform list, although Ansah appears close to a return.

Offensive lineman Darren Keyton left practice prematurely after suffering what appeared to be a right hand/wrist injury during one-on-one drills against the defensive line. Caldwell said he wasn't privy to the seriousness of the injury.